It sounds like your husband may have Obsessive-compulsive disorder (OCD - anxiety disorder) or delusional disorder.
I suspect that he has OCD based on your report.
Let me explain: OCD is an anxiety disorder characterized by unreasonable thoughts and fears (obsessions) that lead you to do repetitive behaviors (compulsions). You feel driven to perform compulsive acts in an effort to ease your stressful feelings, though you may realize your thoughts are unreasonable.
OCD centers around themes, such as a fear of getting contaminated by germs.
It's common for people with OCD to fixate on things or topics and also gets addicted to drugs or alcohol.
I would advise your husband to see his primary care doctor to discuss his obsessions. His doctor may refer him to a psychiatrist for medication consultation and a psychologist for psychotherapy (for OCD management).
I think your husband may accept your request of seeing his doctor first. You may not deny his beliefs as he may believe them.
But, you may tell him that he may have anxiety disorder such as OCD as he may be restless and spends long hours thinking of the foods that may cause his neck pain.
Also, relaxation and Stress
reduction techniques such as yoga, meditation
, Acupuncture, Nutrition and Guided imagery may help him to reduce anxiety symptoms like obsessions and restlessness.
If he is open to psychotherapy, I would advise him to work with a psychologist WEEKLY for 3- 6 months or longer.
Medication and psychotherapy are effective for OCD.
He may benefit from having a Cognitive-Behavior therapy (CBT) for his anxiety disorder/OCD.
You can call his insurance company and get a list of providers in your area.
Or, you can search a licensed psychologist on internet- such as the PSYCHOLOGY TODAY website. Go to (http://therapists.psychologytoday.com/ppc/prof_search.php?iorb=4764) and enter your zip code and optional category of specialty such as OCD. Read psychotherapists’ profile to see if he or she specializes in Cognitive-Behavior therapy (CBT).
You may also want to create your mental image of psychotherapist that you want to work with – Male or female? To note, many therapists offer initial consultation for free. So, he can see it as an informational meeting. He can ask any question.
Please let me know if you have more questions after getting this answer. All the best,